In an agricultural vehicle, there are numerous operations that need to be performed by the use of switches. As a consequence, the space available on the control panel to accommodate the various switches is at a premium. If one has dedicated switches for each of the different functions, inevitably some will need to be located in inconvenient positions for the operator.
It has already been proposed to mitigate this problem by the use of a configurable switch. A multi-function switch is ergonomically positioned and the function that it performs in any mode is determined by the control system to which it is connected. Hence, the same switch can be used in one mode to control a front PTO (power take-off) and in another to control, for example, the operation of the electro-hydraulic remotes.
It is straightforward, especially when the control system is computerized, to modify the way that the switch functions electrically, so that in the example given above its output is sent in the first mode to the front PTO and in another mode to one of the electro-hydraulic remotes.
It is not however sufficient to change the way in which a switch operates electrically, the manner that its control lever moves mechanically needs also to be modified to suit the task at hand, so as to operate in the same manner as a switch dedicated to that task. Depending on the task, one or more of the switch positions may need to be changed from latched to spring biased, also termed a momentary position. If a positioned is latched, the switch acts as an ON/OFF switch and remains in the position in which its control lever is left. If it is momentary, the switch will only remain in an ON position until the control lever is released, whereupon it will automatically return to a neutral rest position.
Configurable switches have previously been disclosed in the prior art, for example in U.S. Pat. No. 4,438,660 and U.S. Pat. No. 4,440,040, in which a switch position can be changed from a latched position to a spring biased position. A switch that is in current production and is believed to represent the closest prior art to the present invention is shown schematically in FIG. 1 of the accompanying drawings.
In FIG. 1, a control lever 10 is pivotably mounted in a switch housing 12 having an external electrical connector 16. Within the housing 12, there is mounted a potentiometer and electrical switch module 18 connected by multiple wires 20 to the connector 16. The internal construction of the switch module 18 is not material to the present invention and it may typically have a wiper arm movable by the control lever 10 which contacts a resistive track to produce a continuously variable resistance on one output lead. In different positions of the control lever 10, the wiper arm closes switch contacts. The variable resistance output of the switch can be used to corroborate the control lever position to safeguard against erroneous states of the switch contacts, caused by a short circuit or an open circuit in the internal wiring of the switch.
The spindle of the control lever 10 that moves the wiper arm of the switch module is connected to a cam plate 22 shown separately in FIG. 2. The cam plate 22 has a cam track 23 defining three notches marked R, F and EF which correspond respectively to a reverse, forward and an extended forward position of the lever 10 and a further section defining a central position N corresponding to a neutral position of the control lever 10. A detent 24 is mounted in the housing 12 for pivoting movement about a pin 27 and is biased towards the cam track 23 by means of a spring plate 26 which is pivotable in the housing 12 about a pin 25. The opposite end of the spring plate 26 rests on a catch 28 which is pivotable in the housing 12 about a further pin 29. A coil spring 30 acts between the catch 28 and the spring plate 26 to urge the latter clockwise as viewed in the drawing. Pivoting of the latch about the pin 29 is effected by means of the armature pin 33 of a solenoid 32 which is connected by further wires 34 to the connector 16.
In FIG. 1, the lever arm is latched in the forward position. The latching is effected by the detent 24 which is biased by means of the spring plate 26 to engage in the notch F in the cam track 23. In the same way, if the control lever 10 is moved to the reverse or extended forward positions, it will be latched in those positions in the same manner. The lever 10 is biased by a separate centering spring into its central neutral position and there is no notch required in the cam plate 22 to latch the lever 10 in the central or neutral position.
To configure the control lever so that it returns to its neutral position whenever it is released, the solenoid 32 is remotely activated to pivot the catch 28 anticlockwise as viewed. The catch 28 will then release the end of the spring plate 26 which will be free to pivot anticlockwise about the pin 25. The detent 24 is now only held against the cam track 23 by the force of the weak spring 30. The centering spring acting on the control lever 10 is able to overcome the force of the detent 24 so that the control lever 10 can no longer be latched by the detent 24 in any of the reverse, forward or extended forward positions. The solenoid 32 can be operated at any time when the control lever 10 is latched so that it can act as an override to return or kick-out the control lever 10 to the neutral position whenever necessary, for example to ensure that the control lever is in the neutral position prior to the engine being started.
Because the position of the control lever 10 is known from the variable resistance output of the switch module, it is possible to engage and disengage the detent 24 as a function of lever position so that, for example, the forward and reverse positioned may be latched and the extended forward position spring biased.
It has been assumed that the same detent 24 engages all three of the notches in the cam track but a further possibility is to have the notches in different planes and engaged by separate detents 24 so that each position of the control lever may be set to latched or momentary independently of the setting of the other positions.
A disadvantage of the described configurable switch is that regardless of its operating mode, the control lever can always be moved to four positions. If a task only requires a two or three position switch, the control lever will have redundant positions and these have been found to be confusing to the operator.